Test tube rack



FIG. 1 is a perspective view of the test tube rack incorporating the teaching of the present invention;

FIG. 2 is a top plan view of one embodiment of the test tube rack;

FIG. 3 is a front view of the test tube rack;

FIG. 4 is a side elevational view of the test tube rack;

FIG. 5 is a rear view of the test tube rack. 

The ornamental design for a test tube rack, as shown and described. 